The invention relates to an interferometric device applied to the measurement of an angular rotational speed by using the Sagnac effect.
An interferometer of the prior art comprises mainly a light energy source generally formed by a laser; an optical device formed either by a certain number of mirrors, or by an optical fiber wound on itself, this device forming a wave guide; a device for separating and mixing the light and a device for detecting and processing the detected signal.
In such an interferometer there exist two waves coming from the separator device and travelling in opposite directions over the same optical path.
A fundamental property of ring interferometers is the reciprocity which may be expressed as follows: any disturbance of the optical path affects the waves similarly although these two waves are not subjected thereto exactly at the same time nor in the same direction.
There exist however two types of disturbance which affect the reciprocity.
On the one hand we have disturbances which vary in time, within a lapse of time comparable to the time that the waves take to propagate along the optical path of the interferometer; and on the other hand, so called "non reciprocal" disturbances, i.e. disturbances not having the same effect on the waves depending on whether they are propagated in one direction or in another along the optical path. It is a question of physical effects which destroy the symmetry of the medium in which the waves are propagated.
Two known effects present this latter type of disturbance:
the Faraday effect, or colinear magneto-optical effect, in which a magnetic field creates a preferential orientation of the spin of the electrons of an optical material, PA1 and the Sagnac effect, or relativist inertial effect, in which the rotation of the interferometer with respect to a Galilean reference destroys the symmetry of the propagation time. This effect is used for constructing more particularly gyrometers or rate gyros.
In the absence of "non reciprocal" disturbances, the phase difference, which will be called .DELTA..phi. hereafter, between the two waves which are recombined in the separation and mixing device after travelling over the optical path, is zero. The detection and processing device detects signals representing the optical power of the composite wave obtained after recombination. This power may be broken down in the interferometers of the prior art into two components: a constant component and a component which only exists on the appearance of "non reciprocal" disturbances.